Greg Procter wrote:
> Nate Nagel wrote:
>
>>Greg Procter wrote:
>>
>>>Nate Nagel wrote:
>>>
>>>
>>>>Greg Procter wrote:
>>>>
>>>>
>>>>>"DanKMTB@
gmail.com" wrote:
>>>>>
>>>>>
>>>>>
>>>>>>On Jul 31, 1:37 pm, "DanK...@
gmail.com"
gmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>>>>>>>>On Jul 31, 1:15 pm, Speeders & Drunk Drivers are MURDERERS
>>>>>>>
>>>>>>>
yahoo.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>>>>>>>>>Bo Raxo wrote:
>>>>>>>
>>>>>>>>>I hit triple digit speeds probably twice a week on average, on my
>>>>>>>>>motorcycle. Never resulted in an accident. Rather proves I can do it
>>>>>>>>>safely.
>>>>>>>
>>>>>>>>Do your kids know that daddy is a kid-killing psychopath?
>>>>>>>
>>>>>>>He said never had an accident. You admit to killing people with your
>>>>>>>vehicle. 100mph is manageable on a crotch rocket easily enough, and
>>>>>>>the crotch rocket will stop faster and turn far better at 100mph then
>>>>>>>your minivan ever will. Does your family know about your killing?
>>>>>>>I refuse to limit my speeds to what you consider safe. Vehicle and
>>>>>>>skill are the deciding factors here.
>>>>>>>You should pay special attention to the "insane" and "over and over
>>>>>>>expecting different results" portions of Bo's posts. You may need to
>>>>>>>sit with someone more patient than me for help comprehending.
>>>>>>
>>>>>>edit: I meant to throw a 50mph qualifier in there for the minivan.
>>>>>>Clearly a minivan @ 5mph will stop faster than the bike @ 100mph, but
>>>>>>bring the van to 50mph and the bike will out-stop or out-handle from
>>>>>>100.
>>>>>
>>>>>
>>>>>That's just silly!
>>>>>Four wheels are always more stable than two.
>>>>>Braking is a combination of stability and energy disipation - an empty
>>>>>van designed to brake a maximum load from 60 mph will stop considerably
>>>>>quicker than a motorcycle from the same speed.
>>>>
>>>>Are you SURE about that? like, really, really sure?
>>>
>>>
>>>I'm really really sure! Physics (the laws of nature) doesn't change just
>>>because one thinks bikes are better than cars, or vice versa.
>>>
>>
>>Agreed.
>>
>>
>>>Braking is a factor of weight, velocity and friction between tyre and
>>>road surface.
>>
>>Nope, only the last.
>
>
> Are you suggesting that braking from (say) 100mph to 60mph is the same
> as braking from 60mph to 0mph?
No, I'm saying that, as I explained in my other post, a vehicle can only
decelerate at a rate in G's equal to the coefficient of friction between
the tire and the road. Any deviation in the real world from that
theoretical statement is due to the non-Newtonian behavior of the
tire/road interface and is small enough to be of interest only to racers.
> Are you suggesting that a Harley Davidson 1200cc would brake just as
> well id fitted with a Honda 50cc front brake?
>
Maybe, maybe not. Probably not. But you're arguing something
completely different than what we started talking about. IME a
motorcycle is far more likely to be factory fitted with more than
adequate (i.e. big enough to generate enough torque to overcome the
friction of the tires, and not fade) brakes than non-sporting passenger
cars or trucks.
>
>>>We eliminated velocity and road surface from the equation by comparing
>>>the two side by side.
>>>That leaves us with weight and tyre area on the road plus stability of
>>>the braking vehicle.
>>>
>>
>>The weight doesn't matter - only the coefficient of friction.
>
>
> Weight to contact patch area matters - coefficient of friction is the
> third factor.
Nope, completely wrong. "weight to contact patch area" = the air
pressure in your tires. What does that have to do with the price of tea
in China?
>
>
>>>A "crotch rocket" is going to be standing on it's front wheel under
>>>maximum braking force and it will have a round or semi-triangular
>>>cross-section tyre so the rubber in the road is fairly small. Say 200kg
>>>on 10cm square area.(100 square cm = 2kg/cm2)
>>>The van is going to have four squareish section tyres on the road with
>>>60-80%% on the front, Say 1000kg on 150 square cm) (450 square cm =
>>>2.2kg/cm2) (and 500kg on 150 square cm) (0.3kg/cm2)
>>>That gives the van more rubber per kg being braked, so better braking
>>>(assuming the brakes can generate the braking horsepower involved)
>>>That's not counting the better stability of four wheels vs two at the
>>>tyres limit of adhesion.
>>
>>But that makes no difference whatsoever. The only things that matter
>>are a) the coefficient of friction between the tire and the road and b)
>>the ability of the vehicle's brake system to generate enough torque to
>>stop at a rate approaching the limit imposed by a).
>
>
> If that were the case then I could stop my van from 100mph by dragging
> my Nike on the road just as quickly as you could stop your pocket-rocket
> by dragging your Adidas on the road.
> Of course weight matters!
But if you were pressing the full weight of the van on your Nike, and I
were pressing the full weight of my bike on my Adidas, and neither shoe
wore through or melted, and the soles of Nike and Adidas shoes had the
same sliding coefficient of friction vs. asphalt, that would be a true
statement. Weight does NOT matter as the very nature of the Newtonian
model of friction takes weight into account in the coefficient of
friction. mu = F/N, or in other words, the coefficient of friction (mu)
is equal to the force (F) required to move an object against a surface,
divided by the normal force (N, or in most cases the weight of the
object.) Since F = ma, when we start talking about accelerations (or
decelerations, which are the same thing) and friction, the weights and
masses end up cancelling each other out. Sure, it takes more force to
stop a heavier object, but that's not what we're talking about here.
We're talking about which object will stop more quickly, not how much
energy has to be dissipated to do it. And the determining factor in
which vehicle will stop more quickly, assuming the brakes are adequate,
is the tires.
>
>>>Load the van with another 1000kg and the bike would win the contest.
>>
>>Weight shouldn't make a difference, unless you're then reaching the
>>limits of brake torque.
>
>
> We're discussing the limits of braking ability here.
> My van won't compete with your bike above 60mph because that is
> approaching the limits of it's braking torque.
> The faster you go the more trorque is required to slow to lower speeds.
Nope, wrong again. It doesn't matter if you're going 20 MPH or 100 MPH,
to decelerate a given vehicle at 1G, you need to apply a force equal
to the weight of the vehicle. How much torque that works out to per
wheel depends on how much weight transfers to the front of the vehicle
(which in turn depends on the wheelbase, the location of the center of
gravity, etc.) and the radius of the wheels, but the basic point is that
that torque will remain the same at any appreciable road speed.
>
>>>Increase the speed and the bike will win (above 100 km/hr) because it
>>>has bigger brakes for it's weight and better airflow for getting rid of
>>>the heat produced.
>>>
>>>Bottom line; if you're riding your bike in a long line of tailgating
>>>traffic you're going to get hit from behind when you brake - if you lose
>>>concentration for a fraction of a second you're going to hit the car in
>>>front and then get hit by the car behind.
>>>If you leave enough safety margin to the car in front someone will
>>>muscle in.
>>>
>>>
>>>
>>>>I'd be willing to bet that the motorcycle's front tire has a higher
>>>>coefficient of friction than whatever's on the van, unless you're in the
>>>>habit of equipping your cargo van with expensive high performance tires.
>>>
>>>
>>>I do - it's a camper van so it never gets heavily laden and I have to
>>>keep up with traffic flows on main roads.
>>>
>>>
>>
>>Are they as good as the tires put on a motorcycle? I doubt it.
>
>
> I don't know as I don't have the manufacturers' data, but the difference
> wouldn't be great.
> The more grip (coefficient of friction) the softer the rubber compound
> and the quicker the wear.
yes. which is why truck tires generally aren't as grippy as motorcycle
tires. Nobody buys a truck to drive it enthusiastically, while truckers
are concerned with low operating cost and low downtime. Motorcyclists
tend to be enthusiasts, and the tires sold are therefore generally
higher-performance but quicker-wearing.
> Tread patterns also make a difference
not really. Not in dry conditions, anyway.
> and motorcycle tyres have to cope
> with large angles of bank, which car tyres don't.
irrelevant.
nate
